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Chip Provides its Own Power

Photonics.comDec 2010
ENSCHEDE, The Netherlands, Dec. 16, 2010 — Microchips that “harvest” the energy they need from their own surroundings, without depending on batteries or electricity from the grid, will now be possible, thanks to scientists in China and The Netherlands.
Researchers from the University of Twente’s MESA+ Institute for Nanotechnology, together with colleagues from Nankai University in China and Utrecht University have for the first time manufactured a microchip with an efficient solar cell placed on top of the microelectronics. They presented their findings at the International Electron Device Meeting held Dec. 5 to 8 in San Francisco.

Placing a solar cell directly on top of the electronics means that the autonomous chip does not need batteries. In this way, a sensor chip, for example, can be produced, complete with the necessary intelligence and even an antenna for wireless communication. However, the chip’s energy use must be well below 1 mW, said the researchers, so the chip can collect enough energy to operate indoors.

Manufacturing the solar cell separately and fitting it on top of the electronics might seem to be the simplest solution, but this is not the most efficient production process. Instead, the researchers use the chip as a base and apply the solar cell to it layer by layer. This method uses fewer materials and ultimately performs better. However, the combination is not trouble-free: There is a risk that the steps involved in producing the solar cell might damage the electronics, reducing their efficiency.

For this reason, the researchers decided to use solar cells made of amorphous silicon or CIGS (copper indium gallium selenide). This manufacturing procedure does not influence the electronics, and this solar cell type also produces sufficient power, even in low light. Tests have shown that the electronics and the solar cells function properly, and the manufacturing process is also highly suitable for industrial serial production with the use of standard processes.
The research was led by Professor Jurriaan Schmitz. The University of Twente’s Semiconductor Components Group collaborated with colleagues from Nankai University in Tianjin, China, and from the Debye Institute of Utrecht University. The work was made possible by the STW Technology Foundation.

The disordered, glassy solid state of a substance, as distinguished from the highly ordered crystalline solid state. Amorphous and crystalline phases of the same substance differ widely in optical and electrical properties.

Metal used in components of the crystalline semiconductor alloys indium gallium arsenide (InGaAs), indium gallium arsenide phosphide (InGaAsP), and the binary semiconductor indium phosphide (InP). The first two are lattice-matched to InP as the light-emitting medium for lasers or light-emitting diodes in the 1.06- to 1.7-µm range, and the last are used as a substrate and cladding layer.

A device for converting sunlight into electrical energy, consisting of a sandwich of P-type and N-type semiconducting wafers. A photon with sufficient energy striking the cell can dislodge an electron from an atom near the interface of the two crystal types. Electrons released in this way, collected at an electrode, can constitute an electrical current.